Rather than being named for the person who actually, you know, wrote it, the Voynich manuscript is named after Wilfrid Voynich, the book dealer who bought the codex back in 1912. This is because no one knows for sure who wrote the thing. As you might have guessed, though, there is no shortage of theories, both plausible and, uh, less so. The most interesting thing about the Voynich manuscript is this: It’s completely indecipherable, but not because it’s, say, illegible.

Almost the entirety of the manuscript’s 240 pages are written with relatively simple-looking characters, which would appear to be part of a language consisting of about 20 or 25 characters. But that language? It’s completely unknown. Despite having been passed around and studied by different owners since the 16th century, no one has ever been able even identify what language the thing is written in, much less actually read it.

A big, ancient book of unreadable text would always be considered a curiosity, but what has caused the Voynich manuscript to become the source of so many hypotheses and theories are the oftentimes bizarre and mysterious illustrations found throughout the codex. Found within the Voynich manuscript are sections that, judging from the illustrations alone, would appear to be dedicated to herbalism, astronomy, biology, cosmology, pharmacology and even various recipes.